In his writing, Daniels frequently argues that the socially liberal and progressive views prevalent within Western intellectual circles minimise the responsibility of individuals for their own actions and undermine traditional mores, contributing to the formation within prosperous countries of an underclass afflicted by endemic violence, criminality, sexually transmitted diseases, welfare dependency, and drug abuse. Much of Dalrymple's writing is based on his experience of working with criminals and the mentally ill.

The writer has been described as a pessimist. In 2010, Daniel Hannan wrote that Dalrymple's work "takes pessimism about human nature to a new level. Yet its tone is never patronising, shrill or hectoring. Once you get past the initial shock of reading about battered wives, petty crooks and junkies from a non-Left perspective, you find humanity and pathos".[4]

In 1991, he made an extended appearance on British television under the name Theodore Dalrymple. On 23 February, he took part in an After Dark discussion called "Prisons: No Way Out" alongside former gangster Tony Lambrianou, Taki Theodoracopolous and others.[11]

Regarding his pseudonym "Theodore Dalrymple", he wrote that he "chose a name that sounded suitably dyspeptic, that of a gouty old man looking out of the window of his London club, port in hand, lamenting the degenerating state of the world".[14]

He is an atheist, but has criticised anti-theism and says that "to regret religion [...] is to regret our civilisation and its monuments, its achievements, and its legacy)".[15] Raised in a non-religious Jewish home, he began doubting the existence of a God at age nine. He became an atheist in response to a moment in a school assembly.[15]

Daniels has also used other pen names, notably "Edward Theberton" and "Thursday Msigwa". As "Edward Theberton", he has written articles for The Spectator from countries in Africa, including Mozambique.[16] He used the name "Thursday Msigwa" when he wrote Filosofa's Republic, a satire of Tanzania under Julius Nyerere.[17] He may also have used another pen name, in addition to his bona fide name.[14]

Daniels began sending unsolicited articles to The Spectator in the early 1980s; his first published work, entitled A Bit of a Myth appeared in the magazine in August 1983 under the name A.M. Daniels.[9]Charles Moore wrote in 2004 that "Theodore Dalrymple, then writing under a different pseudonym, is the only writer I have ever chosen to publish on the basis of unsolicited articles".[18] Between 1984 and 1991 Daniels published articles in The Spectator under the pseudonym Edward Theberton.

Daniels has written extensively on culture, art, politics, education, and medicine – often drawing on his experiences as a doctor and psychiatrist in Africa and the United Kingdom. The historian Noel Malcolm has described Daniels's written accounts of his experiences working at a prison and a public hospital in Birmingham as "journalistic gold",[19] and Charles Moore observed that "it was only when he returned to Britain that he found what he considered to be true barbarism – the cheerless, self-pitying hedonism and brutality of the dependency culture. Now he is its unmatched chronicler."[18]Daniel Hannan wrote in 2011 that Dalrymple "writes about Koestler's essays and Ethiopian religious art and Nietzschean eternal recurrence – subjects which, in Britain, are generally reserved for the reliably Left-of-Centre figures who appear on Start the Week and Newsnight Review. It is Theodore's misfortune to occupy a place beyond the mental co-ordinates of most commissioning editors."[5]

Our Culture, What's Left of It: The Mandarins and the Masses, published in 2005, is another collection of essays in which he contends that the middle class's abandonment of traditional cultural and behavioural aspirations has, by example, fostered routine incivility and militant ignorance among the poor. He examines diverse themes and figures in the book including Shakespeare, Marx, Virginia Woolf, food deserts and volitional underclass malnutrition, recreational vulgarity, and the legalisation of drugs. One of the essays in the book, "When Islam Breaks Down", was named one of the most important essays of 2004 by David Brooks in the New York Times.[20]

In 2009, Dalrymple's British publisher Monday Books announced it was to publish two books. The first, Not With a Bang But A Whimper, appeared in August 2009. It is different from the United States book of the same name, though some of the author's essays appear in both books. In October 2009, Monday Books published Second Opinion, a further collection of Dalrymple essays, this time dealing exclusively with his work in a British hospital and prison.[21]

With Gibson Square Dalrymple then published his most successful book Spoilt Rotten: The Toxic Cult of Sentimentality (2010), which analyses how sentimentality has become culturally entrenched in British society with seriously harmful effects. In 2011, he published Litter: What Remains of Our Culture, followed by The Pleasure of Thinking (2012), Threats of Pain and Ruin (2014), and others.

The cause of much contemporary misery in Western countries – criminality, domestic violence, drug addiction, aggressive youths, hooliganism, broken families – is the nihilistic, decadent and/or self-destructive behaviour of people who do not know how to live. Both the smoothing over of this behaviour, and the medicalisation of the problems that emerge as a corollary of this behaviour, are forms of indifference. Someone has to tell those people, patiently and with understanding for the particulars of the case, that they have to live differently.[23]

Poverty does not explain aggressive, criminal and self-destructive behaviour. In an African slum you will find among the very poor, living in dreadful circumstances, dignity and decency in abundance, which are painfully lacking in an average English suburb, although its inhabitants are much wealthier.[24]

An attitude characterised by gratefulness and having obligations towards others has been replaced – with awful consequences – by an awareness of "rights" and a sense of entitlement, without responsibilities. This leads to resentment as the rights become violated by parents, authorities, bureaucracies and others in general.[25]

One of the things that make Islam attractive to young westernised Muslim men is the opportunity it gives them to dominate women.[26]

Technocratic or bureaucratic solutions to the problems of mankind produce disasters in cases where the nature of man is the root cause of those problems.

It is a myth, when going "cold turkey" from an opiate such as heroin, that the withdrawal symptoms are virtually unbearable; they are in fact hardly worse than flu.[27][28]

Criminality is much more often the cause of drug addiction than its consequence.

Sentimentality, which is becoming entrenched in British society, is "the progenitor, the godparent, the midwife of brutality".[29]

High culture and refined aesthetic tastes are worth defending, and despite the protestations of non-judgmentalists who say all expression is equal, they are superior to popular culture.[30][31][32]

The ideology of the Welfare State is used to diminish personal responsibility. Erosion of personal responsibility makes people dependent on institutions and favours the existence of a threatening and vulnerable underclass.

Moral relativism can easily be a trick of an egotistical mind to silence the voice of conscience.[33]

The root cause of our contemporary cultural poverty is intellectual dishonesty. First, the intellectuals (more specifically, left-wing ones) have destroyed the foundation of culture, and second, they refuse to acknowledge it by resorting to the caves of political correctness.

Beyond and above all other nations in the world, Britain is the place where all the evils summarised above are most clearly manifest.[36]

Making Bad Decisions. About the Way we Think of Social Problems (2006) (Dr. J. Tans Lecture 2006; published by Studium Generale Maastricht, The Netherlands. Lecture read on Wednesday 15 November 2006. ISBN 978-90-78769-01-9)